gediWFMetrics: GEDI full waveform data processing

In rGEDI: NASA's Global Ecosystem Dynamics Investigation (GEDI) Data Visualization and Processing

Description

GEDI full waveform data processing and metrics extraction

Usage

gediWFMetrics(
  input,
  outRoot,
  writeFit = FALSE,
  writeGauss = FALSE,
  bounds = NULL,
  ground = FALSE,
  useInt = FALSE,
  useFrac = FALSE,
  rhRes = 5,
  laiRes = 10,
  laiH = 30,
  noRHgauss = FALSE,
  gTol = 0,
  fhdHistRes = 0.001,
  forcePsigma = FALSE,
  bayesGround = FALSE,
  dontTrustGround = FALSE,
  noRoundCoord = FALSE,
  noCanopy = FALSE,
  dcBias = 0,
  nSig = 0,
  hNoise = 0,
  linkNoise = NULL,
  linkFsig = NULL,
  linkPsig = NULL,
  trueSig = NULL,
  bitRate = NULL,
  maxDN = NULL,
  renoise = FALSE,
  newPsig = -1,
  oldPsig = 0.764331,
  addDrift = NULL,
  missGround = FALSE,
  minGap = NULL,
  photonCount = FALSE,
  pcl = FALSE,
  nPhotons = 2.1,
  photonWind = 200,
  noiseMult = 0.1,
  rhoVrhoG = 1,
  nPhotC = 2.1,
  nPhotG = -1,
  photHDF = FALSE,
  meanN = 0,
  thresh = 1e-14,
  varNoise = FALSE,
  varScale = NULL,
  statsLen = NULL,
  noiseTrack = FALSE,
  sWidth = NULL,
  psWidth = 0,
  msWidth = NULL,
  preMatchF = FALSE,
  postMatchF = FALSE,
  pFile = NULL,
  gWidth = 1.2,
  minGsig = 0.764331,
  minWidth = 0,
  medNoise = FALSE,
  varDrift = NULL,
  driftFac = NULL,
  rhoG = 0.4,
  rhoC = 0.57,
  pSigma = NULL,
  gold = FALSE,
  deconTol = NULL
)

Arguments

input	gedi.level1bSim (may be a list of objects). Simulated waveform input object(s).
outRoot	name. output filename root
writeFit	write fitted waveform
writeGauss	write Gaussian parameters
bounds	minX minY maxX maxY. only analyse data within bounds
ground	read true ground from file
useInt	use discrete intensity instead of count
useFrac	use fractional hits rather than counts
rhRes	r. percentage energy resolution of RH metrics
laiRes	res. lai profile resolution in metres
laiH	h. height to calculate LAI to
noRHgauss	do not fit Gaussians
gTol	tol. ALS ground tolerance. Used to calculate slope.
fhdHistRes	res. waveform intensity resolution to use when calculating FHD from histograms
forcePsigma	do not read pulse sigma from file
bayesGround	use Bayseian ground finding
dontTrustGround	don't trust ground in waveforms, if included
noRoundCoord	do not round up coords when outputting
noCanopy	do not calculate FHD histograms and LAI profiles
dcBias	n. mean noise level
nSig	sig. noise sigma
hNoise	n. hard threshold noise as a fraction of integral
linkNoise	linkM cov. apply Gaussian noise based on link margin at a cover
linkFsig	sig. footprint width to use when calculating and applying signal noise
linkPsig	sig. pulse width to use when calculating and applying signal noise
trueSig	sig. true sigma of background noise
bitRate	n. digitisation bit rate
maxDN	max. maximum DN
renoise	remove noise from truth before applying new noise level
newPsig	sig. new value for pulse width, when lengthening pulse
oldPsig	sig. old value for pulse width if not defined in waveform file, when lengthening pulse
addDrift	xi. apply detector background drift
missGround	assume ground is missed to assess RH metrics
minGap	gap. delete signal beneath min detectable gap fraction
photonCount	output point cloud from photon counting
pcl	convert to photon counting pulsecompressed
nPhotons	n. mean number of photons
photonWind	x. window length for photon counting search, metres
noiseMult	x. noise multiplier for photoncounting
rhoVrhoG	x. ratio of canopy to ground reflectance at this wavelength. Not different from rhoV and rhoG
nPhotC	n. mean number of canopy photons (replaces nPhotons and rhoVrhoG)
nPhotG	n. mean number of ground photons (replaces nPhotons and rhoVrhoG)
photHDF	write photoncounting
meanN	n. mean noise level, if using a predefined mean level
thresh	n. noise threshold, if using a predefined noise threshold
varNoise	use a variable noise threshold
varScale	x. variable noise threshold scale (multiple of stdev above mean to set threshold)
statsLen	len. length to calculate noise stats over for varNoise
noiseTrack	use noise tracking
sWidth	sig. smoothing width, after densoising
psWidth	sigma. smoothing width, before denoising
msWidth	sig. smoothing width, after noise stats, before denoising
preMatchF	matched filter before denoising
postMatchF	matched filter after denoising
pFile	file. read pulse file, for deconvoltuion and matched filters
gWidth	sig. Gaussian parameter selection smoothing width
minGsig	sig. minimum Gaussian sigma to fit
minWidth	n. minimum feature width in bins
medNoise	use median stats rather than mean
varDrift	correct detector drift with variable factor
driftFac	xi. fix drift with constant drift factor
rhoG	rho. ground reflectance
rhoC	rho. canopy reflectance
pSigma	sig. pulse width to smooth by if using Gaussian pulse
gold	deconvolve with Gold's method
deconTol	deconvolution tolerance

Details

a) Metrics descriptions

a.1) Metrics available to GEDI

• gHeight Ground elevation (m) from Gaussian fitting

• maxGround Ground elevation (m) from lowest maximum

• inflGround Ground elevation (m) from inflection points.

• signal top Elevation of first point above noise (may include noise tracking).

• signal bottom Elevation of last return above noise (may include noise tracking).

• cover Canopy cover (fraction) from area of Gaussian fitted ground. Uses rho_v=0.57 and rho_g=0.4.

• leading edge ext Leading edge extent (m), from Lefksy et al (2007).

• trailing edge extent Trailing edge extent (m), from Lefksy et al (2007).

• rhGauss 0-100 RH metrics, 0

• rhMax 0-100 RH metrics, 0

• rhInfl 0-100 RH metrics, 0

• gaussHalfCov Canopy cover (fraction) from double the energy beneath the Gaussian ground. Uses rho_v=0.57 and rho_g=0.4.

• maxHalfCov Canopy cover (fraction) from double the energy beneath the lowest maximum ground. Uses rho_v=0.57 and rho_g=0.4.

• infHalfCov Canopy cover (fraction) from double the energy beneath the inflection point ground. Uses rho_v=0.57 and rho_g=0.4.

• bayHalfCov Canopy cover (fraction) from double the energy beneath the experimental "Bayesian" ground. Uses rho_v=0.57 and rho_g=0.4.

• lon Footprint centre longitude in projection of ALS data (m).

• lat Footprint centre latitude in projection of ALS data (m).

• waveEnergy Total energy within waveform (will be 1 scaled by noise for simulations).

• blairSense Blair's sensitivity metric. Canopy cover at which this SNR would have90

• FHD Foliage height diversity

• niM2 Wenge Ni's biomass metric, equal to the sum of the RH metrics to the power of 2 (unpublished)

• niM2.1 Wenge Ni's biomass metric, equal to the sum of the RH metrics to the power of 2.1 (unpublished)

a.2) Metrics unavailable to GEDI

• wave ID Waveform label, relates to plot name and footprint number.

• true ground Ground elevation (m) from ALS. Centre of gravity of ground points within footprint

• true top Levation of highest point of waveform (m), without noise. Includes pulse blurring.

• ground slope Effective ground slope (degrees), from width of ground return. Includes roughness.

• ALS cover Canopy cover (fraction) from ALS data. Uses rho_v=0.57 and rho_g=0.4.

• rhReal 0-100 RH metrics, 0

• groundOverlap Fraction of ground return overlapping with canopy return. A measure of understorey.

• groundMin Depth of minimum between ground and canopy return. A measure of understorey.

• groundInfl d2y/dx2 of inflection point between ground and canopy return. A measure of understorey.

• pointDense Average ALS point density within GEDI footprint.

• beamDense Average ALS beam density within GEDI footprint.

a.3) System settings

• pSigma GEDI system pulse width, sigma (m).

• fSigma GEDI footprint width, sigma (m).

• linkM Link margin if noise is added (db).

• linkCov Canopy cover at which the above link margin is true (fraction).

• filename Name of input waveform file.

b) Signal processing description

• Gaussian fitting Used for "gHeight", "rhGauss" and "gaussHalfCov". The waveform is denoised (mean+5*sigma, noise tracking to avoid truncation), smoothed (pSigma*0.75) and Gaussians fitted with Levenberg-Marquardt optimisation. The center of the lowest Gaussian containing at least 0.5

• Maximum Used for "maxGround", "rhMax" and "maxHalfCov". The waveform is denoised (mean+5*sigma, noise tracking to avoid truncation), smoothed (pSigma*0.75). The lowest maximum is taken as the ground.

• Inflection points Used for "inflGround", "rhInfl" and "inflHalfCov". The waveform is denoised (mean+5*sigma, noise tracking to avoid truncation), smoothed (pSigma*0.75). The centre of gravity between the lowest two inflection points is taken as the ground.

• Half covers Used for "gaussHalfCov", "maxHalfCov" and "inflHalfCov". Sum energy beneath estimated ground position. Double that is the ground energy. Calculate canopy cover, correcting for rho_v and rho_g.

  cover = \frac{E_{can}}{E_{can} + E_g*\frac{rho_v}{rho_g}}

  Where Ecan is the canopy energy, Eg is the ground energy, rho_v is the vegetation reflectance and rho_g is the ground reflectance.

• Edge extents These are described in: Lefsky, Michael A., Michael Keller, Yong Pang, Plinio B. De Camargo, and Maria O. Hunter. "Revised method for forest canopy height estimation from Geoscience Laser Altimeter System waveforms." Journal of Applied Remote Sensing 1, no. 1 (2007): 013537-013537.

Value

Returns a list of metrics derived from the simulated full waveform. A text file (txt) containing the metrics will be saved in the output folder (outRoot). Please see the details section for checking the definition of the metrics.

See Also

i) Hancock, S., Armston, J., Hofton, M., Sun, X., Tang, H., Duncanson, L.I., Kellner, J.R. and Dubayah, R., 2019. The GEDI simulator: A large-footprint waveform lidar simulator for calibration and validation of spaceborne missions. Earth and Space Science. https://doi.org/10.1029/2018EA000506

ii) gediSimulator: https://bitbucket.org/StevenHancock/gedisimulator/src/master/

Examples

libsAvailable = require(lidR) && require(plot3D)
if (libsAvailable) {
outdir = tempdir()

# Specifying the path to ALS data (zip)
alsfile_Amazon_zip <- system.file("extdata", "Amazon.zip", package="rGEDI")
alsfile_Savanna_zip <- system.file("extdata", "Savanna.zip", package="rGEDI")

# Unzipping ALS data
alsfile_Amazon_filepath <- unzip(alsfile_Amazon_zip,exdir = outdir)
alsfile_Savanna_filepath <- unzip(alsfile_Savanna_zip,exdir = outdir)

# Reading and plot ALS file (las file)
als_Amazon<-readLAS(alsfile_Amazon_filepath)
als_Savanna<-readLAS(alsfile_Savanna_filepath)

# Extracting plot center geolocations
xcenter_Amazon = mean(als_Amazon@bbox[1,])
ycenter_Amazon = mean(als_Amazon@bbox[2,])
xcenter_Savanna = mean(als_Savanna@bbox[1,])
ycenter_Savanna = mean(als_Savanna@bbox[2,])

# Simulating GEDI full waveform
wf_Amazon<-gediWFSimulator(input=alsfile_Amazon_filepath,
                          output=file.path(outdir,"gediWF_amazon_simulation.h5"),
                          coords = c(xcenter_Amazon, ycenter_Amazon))

wf_Savanna<-gediWFSimulator(input=alsfile_Savanna_filepath,
                           output=file.path(outdir,"gediWF_Savanna_simulation.h5"),
                           coords = c(xcenter_Savanna, ycenter_Savanna))

# Extracting GEDI full waveform derived metrics without adding noise to the full waveform
wf_amazon_metrics<-gediWFMetrics(input=wf_Amazon,outRoot=file.path(outdir, "amazon"))
wf_savanna_metrics<-gediWFMetrics(input=wf_Savanna,outRoot=file.path(outdir, "savanna"))

metrics<-rbind(wf_amazon_metrics,wf_savanna_metrics)
rownames(metrics)<-c("Amazon","Savanna")
head(metrics)

# Extracting GEDI full waveform derived metrics after adding noise to the waveform
wf_amazon_metrics_noise<-gediWFMetrics(input=wf_Amazon,
                        outRoot=file.path(outdir, "amazon"),
                        linkNoise= c(3.0103,0.95),
                        maxDN= 4096,
                        sWidth= 0.5,
                        varScale= 3)

wf_savanna_metrics_noise<-gediWFMetrics(
                       input=wf_Savanna,
                       outRoot=file.path(outdir, "savanna"),
                       linkNoise= c(3.0103,0.95),
                       maxDN= 4096,
                       sWidth= 0.5,
                       varScale= 3)

close(wf_Amazon)
close(wf_Savanna)

metrics_noise<-rbind(wf_amazon_metrics_noise,wf_savanna_metrics_noise)
rownames(metrics_noise)<-c("Amazon","Savanna")
head(metrics_noise)

}

rGEDI documentation built on Jan. 19, 2021, 3:01 p.m.